Citrus greening's cost is at $138 million

Florida citrus growers got some good news this week, if their idea of good news is holding pre-harvest fruit losses in greening-infected groves to 30 percent.

Such is the nature of accentuating the marginally positive in the final months of the 2012-13 Florida citrus season, which has seen a historic number of oranges, grapefruit and tangerines fall from trees before they could be picked.

"All of you have seen a lot of fruit drop from the trees this year," Gene Albrigo, emeritus professor of horticulture at the University of Florida's Citrus Research and Education Center in Lake Alfred, told more than 325 growers at a gathering in Avon Park. "My guess is by now it's the worst season we've ever seen."

While other factors may lie behind this season's premature drop problem, he added, greening literally lies at the root.

Greening is a bacterial disease that causes a citrus tree, left untreated, to produce bitter fruit unfit for consumption. In advanced stages, the tree defoliates and dies.

Until the 2012-13 citrus season, Florida growers believed they could keep their trees productive through enhanced fertilization that replaces nutrients that greening appears to rob from the tree and through additional pesticide spraying to kill the Asian citrus psyllid, the bacteria's host and the primary cause of greening's spread.

The unprecedented fruit drop has growers concerned they cannot survive economically until researchers come up with better solutions.

Anti-greening measures have doubled their grove caretaking costs since 2005, when the disease first surfaced in Florida, and now they are losing millions of boxes of fruit before they can sell it to the state's juice processors, who buy 95 percent of the annual orange crop and more than 60 percent of grapefruit.

Albrigo estimated that Florida growers already have lost 18 million boxes of oranges and grapefruit this season to premature drop, at a loss of $138 million. He said growers can expect more losses in the Valencia orange crop, which is harvested through June.

"It looks like the Valencias are accelerating in drop. It appears the trees are crashing," Albrigo said.

Albrigo and Jim Graham, professor of soil microbiology at the Lake Alfred center, agreed that, while enhanced fertilization may replace some lost nutrients, greening causes nutritional deficits in the tree that contribute to premature drop. Once a psyllid infects the tree by feeding on the canopy, Graham said, the bacteria quickly travels down to the root system and "colonizes it well."

Research has shown greening leads to the loss of 27 percent to 40 percent of a tree's root system, leading to an equivalent rate of preharvest drop.

The loss of so many roots means infected trees are less efficient at absorbing water, making them more vulnerable to drought and also enhancing drop, Graham said. Greening also disrupts the tree's ability to distribute carbohydrates, particularly from the leaves to the stem, he said.

Graham's research also shows that good irrigation and nutritional management on infected trees can keep root losses down to about 30 percent and preharvest drop to the same level, he said.

Albrigo's research shows the additional drop this season is coming from trees showing the most decline from greening, he said. But not all groves, even some infected with greening, have experienced high drop rates.

"We need to get information from the growers, particularly on production practices in low and high drop groves," Albrigo said. "I believe we need to put a lot more time in this. It's a $138 million problem in front of us."

Never miss a story

Choose the plan that's right for you.
Digital access or digital and print delivery.